This invention relates to an orthopedic casting material. More specifically, the invention relates to such casting materials which comprise fabric impregnated and/or coated with polyisocyanate prepolymer and which are treated with mineral oil and fluorocarbon polymer powder to reduce the tack, slip and foaming properties of the material during curing.
Most orthopedic casting tapes currently available are produced using curable resins coated on a substrate such as fiberglass, polyester or other synthetic or natural fabrics. For example, orthopedic casting tapes utilizing polyisocyanate prepolymers which react with water to initiate curing to polyurethanes are known. (U.S. No. 4,411,262 to von Bonin et al., U.S. No. 4,502,479 to Garwood et al.) Generally, the polyisocyanate prepolymer comprises the reaction product of an isocyanate and a polyol, which product polymerizes to polyurethane upon contact with water. The prepolymer-treated bandage is soaked in water prior to application to the body member, and the wet bandage is then applied to the body member. After the bandage is applied, the cast is smoothed with a gloved hand and held at certain points until it hardens. Since the resins in the bandage are quite tacky until they cure, the protective gloves worn by the cast applier tend to stick to the bandage. This is disadvantageous since it can lead to unwinding of the cast as layers of the tape pull apart from each other and the cast cannot be molded.
To alleviate the problem of "tackiness" in curable resin-coated bandages, Scholz et al. proposed, in U.S. No. 4,667,661, treating such bandages with certain lubricants to reduce the kinetic coefficient of friction of such sheets to less than about 1.2. The lubricant can be comprised of (a) hydrophilic groups which are covalently bonded to the curable resin, (b) an additive which is incompatible with the curable resin or (c) a combination of (a) and (b). As noted in the Scholz et al. patent (e.g., column 11, lines 21 et. seq.), the bandages treated with such lubricants become very slippery, and molding of the cast becomes easy due to the non-tacky nature of the resin. It is also noted in the Scholz et al. patent (column 8, lines 45-65) that materials such as mineral oil were evaluated as lubricants and, although they did give a non-tacky and even slippery feeling to the surface of the casting tape, which allowed easy application and moldability of the tape to the patient, the effect was transient. On average, Scholz et al. report, such materials lasted only a day to a week, apparently due to the dissolution of the oil into the resin.
It is believed that products embodying the Scholz et al. invention are now commercially available. Users often complain that such bandages, while certainly not possessing the degree of tackiness associated with other prior bandages, are actually too slippery for easy handling and application.
Another problem common with polyurethane prepolymer resin coated or impregnated sheets is foaming of the resin. Foaming occurs when carbon dioxide is released upon reaction of water with isocyanate groups in the resin. Foaming is undesirable since it reduces the porosity of the cast and its overall strength. It has been suggested (U.S. No. 4,667,661) to reduce foaming by adding foam suppressors such as silicone Antifoam A (Dow Corning), DB-100 silicone fluid (Dow corning) to the resin, but the use of very hydrophilic additives to obtain tack-free casting tapes, such as the hydrophilic additives proposed by Scholz et al., exacerbates the foaming problem in the cast.
There therefore exists a need for a bandage material with improved handling properties, i.e., one which is neither too tacky nor too slippery, and with a reduced tendency to foam compred to commercially available products.